<B>Avascular necrosis of bone </B>

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Avascular necrosis of bone

Etiology:

• Any cause of interruption of blood supply can result in bone necrosis.
• Fractures, thrombosis and embolism, injury of vessels due to vasculitis, and hypertension are all associated with bone infarcts.
• Corticosteroid administration is frequently associated with bone necrosis.

Pathogenesis:

• Any interruption of blood supply results in aseptic necrosis of bone.
• The role of steroids in the genesis of avascular necrosis is not understood.

Epidemiology:

• Fairly common.

General Gross Description:

• Necrosis is typically sharply demarked.
• It may involve only the cancellous bone and marrow; because of blood supply from the periosteum, cortical bone is usually not affected.
• The infarct is typically triangular or wedge shaped.

General Microscopic Description:

• As with necrosis due to any cause, avascular necrosis of bone is recognized by the absence of cells in lacunae.
• Necrosis of the marrow space resembles fat necrosis elsewhere and is typified by the presence of bluish, acellular material.
• The blue color is due to the formation of calcium soaps, derived from fatty acids released by breakdown of fat in adipocytes.

Clinical Correlations:

• Bone necrosis causes chronic pain, usually on exercise, subsequently at rest.
• Subchondral infarcts, which result in necrosis of overlying cartilage, can result in severe osteoarthritis.

References:
•Robbins "Pathologic Basis of Disease". (Cotran, Kumar and Robbins, Eds.) 5th Edition. pp 1229.